ive got to make some. how beefy do they need to be? this is for a custom conversion. I was thinking just some strap steel to the throttle body mounting studs would be enough, but....
not boosted. yet. 60 psi rail pressure, v8, 30lb injectors, etc. should make 400 at the rear wheels on efi, vs the 390 I made with a poorly tuned carb setup. mostly street, occasional autocross/dragstrip.
Well....
Lets call each cup just over 1/2", which makes the area of each cup just under .2 in^2. x4 (for each bank) is roughly .8 in^2.
Round that up to 1", and 60psi will be a 60lb load. Which isn't much strapping needed.
The alignment will be more important- can you solder to the rail you have? Get some like flat material, bend it, solder one end to the rail, and bolt down the other end.
Extruded aluminum rails with pre-drilled holes. So it would bolt on at both ends.
So, what are we talking? 1/4 inch thick? 1x1 angle iron?
Being aluminum, I would use that.
And while I'm not doing the math, I would expect that 1/8 would easily hold 60".
So 1/2" width x 1/8" thickness x whatever it takes to bold down would be fine. As long as it's stiff as well.
define stiff, please.
and I think I can easily find 1/8 x 1 or 1/8 x 3/4 aluminum stock. so that should be enough, right?
In reply to Dusterbd13:
strength is about breaking
stiffness is about bending. So it should not bend- you can put a lip on a simple L bracket to stiffen it up quite a lot. That way the alignment of the injectors is maintained.
Chevy uses 6mm bolts threaded into crappy inserts in plastic manifolds, so take of that what you will.
You really don't have to worry about the pressure of the spray as the total mass exiting the injector is small even at WOT. What you have to do is mount it so that it is not subject to vibration. That can brake the mounting brackets and then shake the rail free causing a fuel leak and fire. Brackets have to be strong enough to withstand the vibrations of the motor x2. Brackets designed to this standard will far exceed any pressure generated by the fuel being sprayed.
In reply to alfadriver:
I have held injector rails at WOT with 4 injectors at full spray. First off 60lb is not the force of the spray it I the volume of fuel flowing through the injector at a fixed duty cycle (usually 80%). So a 60lb injector flows 60 lbs of fuel per hour at 80% duty cycle. The pressure on the rail is mass times velocity squared.
So calculate the volume of fuel times its velocity squared when it exits the injector and it will give you the force it exerts back against the injector and the rail. This number is very small. Hell I can run my Porsche with the injectors in place but the rail not fastened to anything. It stays in place just fine as long as the motor does not shake it free.
In reply to dean1484:
The fuel pressure is the significant force. The flow is a nominal load that the seals can probably hold.
But somewhere in the system, the 60psi of fuel rail pressure is in-between the rail and the injector, and they need to be held together.
Ahhh ok I see. Most rails have clips that hold the injectors to the rail. I was not thinking of that end of things. Then yes there is a force there if the hold downs on the rail are also holding the injectors in to the rail. That must also be a very small force as the clips used on my Porsche are small thin pieces of metal that engage a small slot in the top of the injector. It would be interesting to see what that is but it must be minimal psf.
In reply to dean1484:
You'd be surprised how much load a small strip of metal can hold. 60lb isn't much to it.
DI systems are now operating in the 3000psi range- so that's a lot more force.
I have run over 120psi base fuel pressure through a 1/2" rail bolted down with two M4 bolts through the rail. Just make sure the rail is close enough to the injector cup in the manifold that the injectors can't "push" out of the rail.
dean1484 wrote: So calculate the volume of fuel times its velocity squared when it exits the injector and it will give you the force it exerts back against the injector and the rail. This number is very small. Hell I can run my Porsche with the injectors in place but the rail not fastened to anything. It stays in place just fine as long as the motor does not shake it free.
It's not just the force of the fuel being sprayed, it's also the force of the pressure inside the rail that's trying to push the injectors out of their mounting holes. That force is fuel pressure * area of the back of the injectors.
But yes, I agree, vibration is the most critical part here.
codrus wrote:dean1484 wrote: So calculate the volume of fuel times its velocity squared when it exits the injector and it will give you the force it exerts back against the injector and the rail. This number is very small. Hell I can run my Porsche with the injectors in place but the rail not fastened to anything. It stays in place just fine as long as the motor does not shake it free.It's not just the force of the fuel being sprayed, it's also the force of the pressure inside the rail that's trying to push the injectors out of their mounting holes. That force is fuel pressure * area of the back of the injectors. But yes, I agree, vibration is the most critical part here.
With most factory rails the injector is clipped to the rail with a positive connection so the forces in the rail pushing on the injector are contained by that (or at least should be) If you have a set up where the hold downs for the rail also hold the injectors in the rail and in to the head than yes they are dealing with a bit more pressure.
alfadriver wrote: In reply to dean1484: You'd be surprised how much load a small strip of metal can hold. 60lb isn't much to it. DI systems are now operating in the 3000psi range- so that's a lot more force.
Anyone ever pulled a motor and forgotten a ground strap? This mofos can hold up a a few tons of car! 
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